Catalyst Chemical State during CO Oxidation Reaction on Cu(111) Studied with Ambient-Pressure X-ray Photoelectron Spectroscopy and Near Edge X-ray Adsorption Fine Structure Spectroscopy

Abstract

The chemical structure of a Cu(111) model catalyst during the CO oxidation reaction in the CO+O2 pressure range of 10-300 mTorr at 298-413 K was studied in situ using surface sensitive X-ray photoelectron and adsorption spectroscopy techniques [X-ray photoelectron spectroscopy (XPS) and near edge X-ray adsorption fine structure spectroscopy (NEXAFS)]. For O2:CO partial pressure ratios below 1:3, the surface is covered by chemisorbed O and by a thin (∼1 nm) Cu2O layer, which covers completely the surface for ratios above 1:3 between 333 and 413 K. The Cu2O film increases in thickness and exceeds the escape depth (∼3-4 nm) of the XPS and NEXAFS photoelectrons used for analysis at 413 K. No CuO formation was detected under the reaction conditions used in this work. The main reaction intermediate was found to be CO2(δ-), with a coverage that correlates with the amount of Cu2O, suggesting that this phase is the most active for CO oxidation.

Metal/oxide interfacial effects on the selective oxidation of primary alcohols

“…The adsorption of benzyl alcohol is enhanced by 0.8 eV at CuO x /Ag interface in comparison with Ag(111) (−1.06 eV); and the barrier of O-H scission is largely diminished (below 0.1 eV), comparing the much higher barrier on Ag(111) (1.56 eV). The STM and DFT results demonstrate a similar role of Cu 2 O–Ag interface as FeO–Pt interface in enhancing the adsorption and activation of benzyl alcohol molecules26.…”

Subsurface oxide plays a critical role in CO 2 activation by Cu(111) surfaces to form chemisorbed CO 2 , the first step in reduction of CO 2

“…C-O bonds fall instead in the middle region, namely between 530.8 eV and 532.0 eV. Within this range, from lower to higher BE, we identify chemisorbed CO2, C-O(H), and formate (HCOO−) overlapping at 530.8 eV; l -CO2 at 531.4 eV; and carbonates at 531.8 eV (15,25). Finally, at high BE we observed adsorbed H2O (H2O ads ) at 532.4 eV (15,25).…”

“…As with C 1s, we partition the O 1s spectral window into three regions. At low BEs we identify the states of O bonded as follows: (i) surface adsorbed O (Cu-O ads )on metallic Cu and on suboxidic Cux O structures (Cux O-O ads ) at 531.0 eV and 529.6 eV, respectively (15,(25)(26)(27); (ii) subsurface adsorbed O (O sub ) on metal Cu (Cu-O sub ) at 529.8 eV (27) (as we discuss in a later section, such a presence of suboxide plays an important role in stabilizing the l -CO2); and (iii) for Cux>1O the O 1s is centered at 530.3 eV (15,18,25). It is noteworthy that O ads groups on the Cu surface can serve as nucleation sites for hydroxylation when in the presence of H2O.…”

Probing Electronic Structures of Organic Semiconductors at Buried Interfaces by Electronic Sum Frequency Generation Spectroscopy

“…It is difficult to directly extend the vacuum techniques into measurements under atmosphere. Only some recent advances in differential pumping allow photoelectron spectroscopic techniques to study surfaces under ambient condition (a few Torr) 18 .…”